1. Field of the Invention
The invention relates to a turbomachine having a housing and a rotor mounted radially and axially in the housing. The rotor has a shaft and at least one impeller attached to the shaft. The turbomachine can be structured as a rapidly running flow machine with axial or radial through-flow, and serves for transport, expansion and/or compression of a medium.
2. The Prior Art
A turbomachine structured as a turbocompressor, having the characteristics described above, is described in German Patent No. DE 100 03 018 A1. The rotor is formed from a shaft and an impeller of the turbocompressor disposed at one shaft end, in an overhung manner. The shaft, which can be driven by a gear mechanism, is mounted in the housing on radial slide bearings. Simple slide rings are provided on the shaft to guide the shaft. The rings are disposed on both sides of a gear mechanism pinion of the shaft, and act together with ring surfaces of a drive gear wheel as axial thrust limiters. In order to compensate for the forces that act on the shaft in the axial direction, a pressure chamber is provided at the end of the shaft that lies opposite the impeller. The pressure prevailing there exerts a force that acts on the shaft in the axial direction. In order to compensate for the axial forces that act on the shaft as much as possible, the pressure in the pressure chamber is regulated as a function of the pre-pressure of the turbocompressor. Since the indirect determination of the axial force from the prevailing pre-pressure is subject to a certain amount of uncertainty, increased friction wear of the axial guide can occur, since it is typically not suitable for absorbing great axial forces. Furthermore, the relationships between pre-pressure and the resulting axial force must be determined for every type of machine, in a complicated manner, since they are greatly dependent on the design conditions of the turbomachine. Finally, rapid changes in the operational state also cannot be compensated, due to the inertia of the system, and can lead to destruction of the axial guide formed from slide rings.
German Patent No. DE 101 38 056 A1 relates to a turbomachine having an expansion turbine stage and a turbocompressor stage. The rotor is formed by an impeller of the expansion turbine stage, an impeller of the turbocompressor stage, and a shaft. The impellers are each disposed in an overhung manner on a shaft end, and radial flow can take place through them. The shaft is mounted in the housing on roller bearings, and a force measurement device is disposed between a bearing ring of a roller bearing and an assigned contact surface of the housing. To compensate the forces that act on the roller bearings in the axial direction, a sealed pressure chamber is formed between the back of the impeller and the adjacent housing surface, at least on the back of one of the impellers. The pressure in the pressure chamber is regulated as a function of the measurement value of the force measurement device, in order to compensate the axial forces that act on the shaft. Mounting of the rapidly rotating rotor of the turbomachine requires a precisely aligned and therefore complicated orientation of the roller bearings in the housing. The expansion of the housing in case of temperature variations or temperature gradients during operation of the turbomachine must also be taken into consideration. While the roller bearings shown are suitable for absorbing great forces in the radial direction, even comparatively slight axial stresses can already lead to destruction of the roller bearings.
A single-stage compressor is described in U.S. Pat. No. 5,741,116, the shaft of which is connected with an impeller on one end. Furthermore, two bearing rings as well as two tilt segment bearings assigned to the bearing rings are disposed on the shaft. The two tilt segment bearings each work together with an assigned contact surface. Furthermore, two spring elements are disposed between the two contact surfaces and the compressor housing, around the shaft. Axial forces that act non-uniformly on the impeller are transferred to the bearing rings by way of the shaft, and passed on to the tilt segment bearings. The tilt segment bearings pass these axial forces on to the contact surfaces, from where they are transferred to the spring elements. The spring elements pass the axial forces on to the compressor housing, in which they are deflected axially in proportion to the force acting on them. If a bearing ring is subject to too much stress, the spring element assigned to this bearing ring is therefore deflected more than the other, so that the load is displaced onto the second bearing ring.
U.S. Pat. No. 4,578,018 relates to a gas turbine having a device for balancing out a non-uniform axial pressure that acts on the turbine rotor. In operation, the rotor is exposed to forces that engage axially, which occur due to static or dynamic forces on the various components of the rotor. The axial pressure is transferred to the bearing housing and the machine frame elements by the rotor and an axial slide bearing arrangement. In this connection, the amount of the axial pressure can be recorded by an expansion measurement device affixed to the bearing housing. The signal of this expansion measurement device is amplified and passed on to a regulator that automatically regulates the pressure of a hydraulic fluid that is passed into a pressure chamber behind the rotor, and thus is able to balance out the axial pressure that acts on the rotor.